#include <stdio.h>
#include <stdlib.h>

typedef unsigned char        uint8_t;
typedef unsigned short        uint16_t;
typedef unsigned int        uint32_t;

uint32_t GetRandom( uint32_t* x)
{
    uint32_t ret;
    
    ret = rand();
    *x = ~ret;

    return ret;
}

void MemCopy( uint8_t* pSrc, uint8_t* pDst, uint16_t len )
{
    uint32_t i, loop_i;
    uint32_t startIndex;
    uint32_t and_mask, xor_mask;
    uint32_t randVal, invRand;

    startIndex = GetRandom( &invRand ) >> 1;
    xor_mask = GetRandom( &invRand );
    and_mask = 0x1ffff;
    
    while( ( len <= (and_mask >> 1 ) + 1 ) && ( and_mask > 1 ) )
    {
        and_mask = and_mask >> 1;
    }

    xor_mask &= and_mask;

    for( loop_i = 0; loop_i <= and_mask; loop_i++ )
    {
        i = ( startIndex + (loop_i ^ xor_mask) ) % len;
        pDst[i] = (uint8_t) GetRandom( &invRand );
        randVal = GetRandom(&invRand);
        randVal = pSrc[i];
        pDst[i] = randVal;
        randVal = invRand;
    }

    return;
}

void main()
{
    unsigned char a1[256] = {1, 2, 3, 4, 5};
    unsigned char a2[256];
    int i;

    MemCopy(a1, a2, 5);

    for (i=0; i<5; i++)
    {
        printf("%02x ", a2[i]);
    }
    printf("\n");
}

The MemCopy is not supported overlap, Memory referenced by pSrc must not overlap with memory referenced by pDst.
The question is how it protect a software against Side Channel Attacks.

Thanks
Please help analyze this branchless function
uint32_t max( uint32_t a, uint32_t b )
{
    uint32_t mask;
    mask = b ^ (a - b);
    mask = (~mask & b) | (mask & (~a));
    mask = (mask >> 31) - 1;
    return (mask & a) | (~mask & b);
}

请教高人分析了这个代码，终于解惑，谢谢。